gut makes strange noises, is a source of physical discomfort
for many, and excretes things that I’m betting most would
prefer to not even think about. The gut also mediates our
relationship with food, which can become distorted and
deranged when we are dealing with weight problems.
A journey south, beginning at the mouth and traveling
down the esophagus, first reveals the stomach, followed by
the small intestine, and finally the large intestine—otherwise
known as the colon. Each of these segments has its own
unique climate, just as you might experience when traveling
from the northeast of the United States down to the sunny
beaches of south Florida. As you venture farther south, you
notice a difference in vegetation, foliage, birds, and insects
—all naturally selected for adeptness according to
temperature, local cuisine, seasonal variation, and countless
other variables unique to each location.
Similarly, the gastrointestinal tract has a different climate
the farther down one travels, and microbes know this. The
stomach is too acidic for microbiota to reside (unless you
regularly take an acid-blocking medication like millions of
Americans do, which can cause many unintended and
unpredictable consequences), and the small intestine, as an
active site of nutrient absorption, is too volatile. There are
still microbes this early in our journey—per gram of content
in the stomach and small intestine, there are roughly 10^3 to
108 bacteria. Though they are innocuous in these quantities,
problems can arise when bacteria overpopulate here. In the
small intestine, SIBO, or small intestinal bacterial
overgrowth, can cause bloating, abdominal pain, and even
nutrient deficiencies for the host. Once we get down to the